Effect Of Interfacial Strain Research Articles

Epitaxy of Antimonene Thin Films with Screw Dislocations for the Application of Saturable Absorbers.

The exotic optoelectronic properties of antimonene, including strain-induced tunable bandgaps, broad nonlinear refractive response, etc., have evoked profound upsurges for decades. As the screw dislocations break the crystal symmetry and modify interlayer coupling, it is highly desirable to investigate the optical prospects of antimonene with screw dislocations. Herein, controllable epitaxy of spiral β-antimonene is achieved on Fe3GaTe2 substrates. By fine-tuning growth temperatures, the evolutions of spiral β-antimonene with non-centrosymmetric stacking are investigated via scanning tunneling microscopy. The effects of interfacial strain and dislocation motion during screw-dislocation-driven growth are also studied. Additionally, a modulation depth of 40.8% and mode locking at 1558 nm with a pulse width of 290 fs are observed in Er-doped pulsed fiber lasers generated with spiral Sb-based saturable absorbers, revealing superior performance that far outstrips reported Sb-based saturable absorbers to date. Our work sheds light on the preparation of Sb films with screw dislocations and demonstrates a promising approach toward fabricating ultrafast optical devices.

Magnetotransport, spin reorientation, and anomalous ferrimagnetic-to-antiferromagnetic phase transition in epitaxial Mn2Sb alloy thin films

High-quality ferrimagnetic Mn2Sb epitaxial thin films have been successfully grown on SrTiO3 (001) single-crystal substrates via systematically optimizing the growth parameters using molecular beam epitaxy. Magnetotransport and magnetic measurements reveal that a spin reorientation transition occurs in the 260–150 K region where the direction of spins rotates from out-of-plane to in-plane upon cooling, resulting in the ferrimagnetic(II) phase, followed by a giant magnetoresistance associated anomalous ferrimagnetic(II)-to-canted antiferromagnetic (c-AFM) phase transition in the 150–115 K region, resulting in the c-AFM ground state, both of which are completely absent and have yet not been previously observed in Mn2Sb bulk and thin films. Temperature-dependent X-ray diffraction measurements reveal that the low-temperature c-AFM phase originates from the contraction of the out-of-plane lattice constant c, which would increase the exchange interaction between neighbouring magnetic sublattices and thus stabilize the c-AFM phase. DFT calculations reveal that substrate clamping is the cause of the unique c-axis contraction in Mn2Sb films. For the 24-nm films, there is almost no out-of-plane magnetization in the ground state, but exists a weak in-plane remanent magnetization (∼0.4 μB/f.u.) and anomalous Hall effects, implying spin canting within the ab plane. With decreasing film thickness from 64 to 8 nm, the out-of-plane saturation magnetization at 10 K increases by approximately 10 times, and for the 8-nm film, its saturation magnetization (4.8 μB/f.u.) is 2.8 times larger than that of Mn2Sb bulk (∼1.74 μB/f.u.), both of which are attributed to the interfacial strain effect. Our work demonstrates that Mn2Sb films grown on perovskite oxide substrates show anomalous spin-charge-lattice coupling phenomena, which may inspire more study of its basic properties and potential device applications.

Tuning Ionic Conductivity in Fluorite Gd-Doped CeO2-Bixbyite RE2O3 (RE = Y and Sm) Multilayer Thin Films by Controlling Interfacial Strain.

Interfacial strain in heteroepitaxial oxide thin films is a powerful tool for discovering properties and recognizing the potential of materials performance. Particularly, facilitating ion conduction by interfacial strain in oxide multilayer thin films has always been seen to be a highly promising route to this goal. However, the effect of interfacial strain on ion transport properties is still controversial due to the difficulty in deconvoluting the strain contribution from other interfacial phenomena, such as space charge effects. Here, we show that interfacial strain can effectively tune the ionic conductivity by successfully growing multilayer thin films composed of an ionic conductor Gd-doped CeO2 (GDC) and an insulator RE2O3 (RE = Y and Sm). In contrast to compressively strained GDC-Y2O3 multilayer films, tensile strained GDC-Sm2O3 multilayer films demonstrate the enhanced ionic conductivity of GDC, which is attributed to the increased concentration of oxygen vacancies. In addition, we demonstrate that increasing the number of interfaces has no impact on the further enhancement of the ionic conductivity in GDC-Sm2O3 multilayer films. Our findings demonstrate the unambiguous role of interfacial strain on ion conduction of oxides and provide insights into the rational design of fast ion conductors through interface engineering.

Effect of steric hindrance on the interfacial connection of MOF-on-MOF architectures.

MOF-on-MOF is attracting great attention due to its improved and/or synergistic properties not exhibited in a single MOF. In particular, the non-isostructural pairs of MOF-on-MOFs can have great potential induced by large heterogeneity, which enables diverse applications in a wide range of fields. HKUST-1@IRMOF is a fascinating platform because the alteration of the IRMOF pores with bulkier substituent groups on the ligands can provide a more microporous environment. However, the sterically hindered linker can affect the seamless growth at the interface, an important issue in practical research fields. Despite many efforts to reveal the growth of a MOF-on-MOF, there is still a lack of studies on a MOF-on-MOF consisting of a sterically hindered interface. Indeed, the effect of a bulky linker at an interface of HKUST-1@IRMOF, a non-isostructural MOF-on-MOF system, has not yet been reported, and thus, how the interfacial strain affects the interfacial growth remains unknown. In this study, we investigate the effect of an interfacial strain on a chemical connection point in an MOF-on-MOF system through a series of theoretical and synthetic experiments using a HKUST-1@IRMOF system. Our results reveal the importance of the proximity of each coordinating site at a MOF-on-MOF interface as well as lattice parameter matching for an effective secondary growth to achieve a well-connected MOF-on-MOF.

A realistic model of temperature dependent carrier diffusion constant in MAPbI3 films

The charge carrier mobility in perovskites is known to be affected by temperature. However, at low temperatures the perovskite film bears interfacial strains by deformation between the film and its substrate with difference coefficients of thermal expansion. Herein we provide a more realistic temperature-dependent carrier dynamics model involving both interfacial strain effect and intrinsic optoelectronic properties. The interfacial strain of a MAPbI3 film is confirmed through in-situ temperature-dependent X-ray diffractions. The carrier dynamics at different temperatures are unraveled using carrier dynamics fittings to time-resolved photoluminescence decays. An abnormal drop in carrier mobility is revealed with continuously decreasing temperature. The strain affects the trap density in films thus declines the carrier mobility at low temperatures. The carrier losses at the buried surface become significant at low temperatures due to the interfacial strain. This work provides a reminder that substrates should be carefully considered in temperature-related applications of perovskites.

Evidence of Delta Phase of Fe in MBE-Grown Thin Epitaxial Films on GaAs

Fe/GaAs is an important system for the study of spin injection behavior that can vary with the nature and interfaces of Fe films. Here, we investigate the effect of interfacial strain on the microstructure, interfaces and phase-formation behavior in epitaxially grown Fe films. To vary the strain, we have characterized Fe films of various thicknesses ranging from 10 to 1000 nm which were grown using molecular beam epitaxy on GaAs (011) and AlGaAs (001) substrates. High resolution X-ray diffraction studies revealed that films with higher thicknesses exhibited an equilibrium α-Fe phase, while the films with less than 10 nm thicknesses indicated the presence of δ-Fe. Transmission electron microscopy revealed the interface for 10-nm-thick films had strain lobes with no interfacial phase formation for films deposited at room temperature. At a higher deposition temperature of 175 °C, similar strain lobes were observed for a 10-nm-thick film. Extended annealing at 200 °C transformed the metastable δ-Fe phase to an equilibrium α-Fe. However, at higher temperature, the interface contained an intermixing layer of (FeAl)GaAs. We demonstrate that the interfacial strain plays a major role in stabilizing the metastable δ-Fe on GaAs.

Strain‐Induced Large Anomalous Nernst Effect in Polycrystalline Co2MnGa/AlN Multilayers

AbstractThe anomalous Nernst effect (ANE), one of the thermoelectric effects in a magnet, is recently attracting growing interest with its potential for the next generation high‐efficiency energy‐harvesting applications. However, the reported thermoelectric conversion efficiencies with ANE are small compared to those with Seebeck effect, which hampers its practical application. Unlike the intensive effort of seeking novel materials with large intrinsic ANE, here a new pathway is proposed to enhance the ANE by exploiting the strain induced in a multilayer structure. A large anomalous Nernst coefficient of 4.9 µV K−1 is achieved for a polycrystalline Co2MnGa/AlN multilayer film deposited on an amorphous substrate, which is larger than 3.8 µV K−1 for a polycrystalline Co2MnGa single layer film. The enhanced ANE is attributed to the effect of interfacial strain on the Seebeck coefficient, which is barely discussed yet. Since the AlN layer is available on any substrate materials, even on a flexible polyimide substrate large ANE is successfully achieved for the Co2MnGa/AlN stack. The findings and demonstration have opened a way to develop the ANE‐based potential applications.

(Invited) Strain Effects on Li Ion Conductivity – Migration, Defect Correlations, and Structural Changes

Elastic or plastic strain at cathode/electrolyte interfaces can affect the charge transfer kinetics in all-solid-state Li-ion batteries. Quantifying this effect both for Li ion conduction within the solid electrolyte material and for the Li transfer ability at the interface is important for understanding the kinetics of solid state batteries. Depending on the strain tensor, the impact could be beneficial or, alternatively, detrimental. While it is generally known that isotropic tensile strain increases the ionic conductivity and compressive strain decreases it [1], how different strain fields act upon Li ion conduction is not yet assessed. Existing studies show a non-trivial decrease/increase of Li-ion migration energies depending on relative alignment of migration direction and strain field [2], making quantitative estimates of conductivity changes difficult to predict. Here, we study the effect of strain on Li ion conductivity of β-Li3PS4 by means of Ab Initio Molecular Dynamics (AIMD) simulations. Ionic conductivity is directly calculated from AIMD trajectories using Nernst–Einstein equation, as it is linearly proportional to the diffusivity of the center-of-mass of all Li-ions [3]. Our calculations indicate that biaxial strain could substantially promote correlated motions of Li-ions, which in turn could increase ionic conductivity of β-Li3PS4. The effect depends on direction of applied strain, and the underlying structural changes increasing ionic conductivity are discussed.[1] Y. Wang, W.D. Richards, S.P. Ong, L.J. Miara, J.C. Kim, Y. Mo and G. Ceder, Design principles for solid-state lithium superionic conductors, Nat. Mater. 14 , 1026–1031 (2015)[2] C. O’Rourke and B. Morgan, Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl2O4, Phys. Rev. M 2, 045403 (2018)[3] A. Marcolongo and N. Marzari, Ionic correlations and failure of Nernst-Einstein relation in solid-state electrolytes, Phys. Rev. M 1, 025402 (2017)

Impacts of Microstructures on the Ionic Diffusivity of Solid Electrolytes: Mesoscale Modeling Approach

Development of viable solid electrolytes is key for commercial adoption of all-solid-state batteries that can solve critical issues associated with electrochemical stability and safety for wider scale applications of the current battery technology. Recent years have seen the emergence of several solid electrolyte candidates with high ionic conductivity; however, practical processing and synthesis routes often generate internal interfaces that can disrupt conduction channels in these materials. In this talk, we will present our development of an efficient mesoscopic computational method for predicting the effective diffusivity through a solid electrolyte with a complex polycrystalline or polygranular microstructure. Our method considers simultaneous interfacial and bulk conduction modes, going far beyond simplified circuit descriptions to account for factors such as orientational variation of crystallite domains and the effects of interfacial strain. Using the Li7La3Zr2O12 (LLZO) solid electrolyte as a model system, we show how our simulation framework can be parameterized using a multiscale approach that derives digital microstructures from phase-field simulations and diffusivity tensors of reference phases and boundaries from molecular dynamics simulations. Simulations of the effective diffusivity of polycrystalline LLZO are applied to investigate the relationship between relevant microstructural features and ionic conductivity, with a focus on topological features of grains and grain networks. Using several instances, we will discuss a high sensitivity to these features, highlighting the need to account for microstructure when assessing mass transport in LLZO and related solid electrolyte materials. This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Temperature Dependent Electric Properties and Magnetoelectric Effects in Ferroelectric rich Ni0.8Mg0.2Fe2O4 + BaZr0.2Ti0.8O3 Magnetoelectric Composites

The magnetoelectric composites with the compositions of ferrites & ferroelectrics having the general chemical formula (x) Ni0.8Mg0.2Fe2O4 + (1-x) BaZr0.2Ti0.8O3 (in which x = 0.1, 0.2, 0.3) were synthesized by using double sintering ceramic technique. From XRD, the phase formation of ferrites with cubic structure and ferroelectrics with tetragonal perovskite structure was confirmed through the measurement of XRD. The two phase ME composites have larger saturation magnetization and dielectric constant; it is because of the effect of interfacial strain on BaZr0.2Ti0.8O3 ferroelectric phase. Furthermore, the ME response 4.262 mVcm−1Oe−1 was observed for (30%) Ni0.8Mg0.2Fe2O4 + (70%) BaZr0.2Ti0.8O3 composites at 5.0 kOe applied DC magnetic field; it shows the success of magnetic control of the dielectric response via the mechanical coupling which can be exploited in the future applications of multiferroic composites.

Electrically Driven Reversible Magnetic Rotation in Nanoscale Multiferroic Heterostructures.

Electrically driven magnetic switching (EDMS) is highly demanded for next-generation advanced memories or spintronic devices. The key challenge is to achieve repeatable and reversible EDMS at sufficiently small scale. In this work, we reported an experimental realization of room-temperature, electrically driven, reversible, and robust 120° magnetic state rotation in nanoscale multiferroic heterostructures consisting of a triangular Co nanomagnet array on tetragonal BiFeO3 films, which can be directly monitored by magnetic force microscope (MFM) imaging. The observed reversible magnetic switching in an individual nanomagnet can be triggered by a small electric pulse within 10 V with an ultrashort time of ∼10 ns, which also demonstrates sufficient switching cycling and months-long retention lifetime. A mechanism based on synergic effects of interfacial strain and exchange coupling plus shape anisotropy was also proposed, which was also verified by micromagnetic simulations. Our results create an avenue to engineer the nanoscale EDMS for low-power-consumption, high-density, nonvolatile magnetoelectric memories and beyond.

Crystal structure, magnetic and dielectric properties of (1-x) BiFe0.80Ti0.20O3 – (x)Co0.5Ni0.5Fe2O4 multiferroic composites

(1-x)BiFe0.80Ti0.20O3–(x)Co0.5Ni0.5Fe2O4 multiferroic composites (x = 0.0, 0.3, 0.5, 0.7 and 1.0) was synthesized by the tartaric acid modified sol-gel method. The Rietveld refinements of all XRD patterns have been carried out to obtain the phase percentages of perovskite BiFe0.80Ti0.20O3 and spinel Co0.5Ni0.5Fe2O4. A change in the lattice parameters of the BFTO and CNFO phase in the composites have been observed, which could be due to strain at the interface of BFTO and CNFO. A change in the peak positions in the Raman spectra of BFTO and CNFO in the composite has been observed and it is well correlated with the XRD results. A significant increase in the magnetization has been observed due to incorporation of Co0.5Ni0.5Fe2O4 phase in the composite. Vegard's law was used to calculate the theoretical value of magnetization for all the composites and compared with the experimental value. Excess value of magnetization observed in the experimental data of composites as compared to the theoretically calculated value and, explained on the basis of interfacial strain effect. An enhancement in the dielectric properties has been observed in the composite system. A correlation between the structure, magnetic and dielectric properties has been reported by assuming strain at the interface of BFTO and CNFO phase.

Lattice strain induced multiferroicity in PZT-CFO particulate composite

Lead Zirconate Titanate [Pb(Zr0.52Ti0.48)O3/PZT] and Cobalt Ferrite [CoFe2O4/CFO] based multiferroic composites [(1-x)PZT-(x)CFO] with (x = 0.10–0.40) have been prepared to study its magnetoelectric (ME) and multiferroic properties. X-ray diffraction method along with the Rietveld refinement technique reveals that the crystal symmetries corresponding to PZT and CFO exist independently in the composites. The effect of interfacial strain on lattice distortion in PZT has been observed. It is well correlated with the magnetoelectric coupling of the composites. Dispersion behavior of dielectric constant with frequency can be explained by the modified Debye model. Different relaxation phenomena have been observed in PZT-CFO particulate composites. The ferroelectric properties of composites decrease with the increase in percentage of CFO in the composite. Both saturation (Ms) and remanent (Mr) magnetization increase with the increase in CFO content in the composite. The maximum ME coupling was found to be 1.339 pC/cm2 Oe for the composition (0.80) PZT-(0.20) CFO at the application of maximum magnetic field of 50 Oe. The multiferroic properties in CFO-PZT can be explained by the lattice strain at the CFO-PZT interfaces.

Phase Transition-Promoted Hydrogen Evolution Performance of MoS2/VO2 Hybrids

In this work, MoS2/VO2 hybrids were synthesized using a two-step hydrothermal method. We used tungsten doping to stabilize the VO2 into the rutile phase at room temperature. The VO2 surface was treated using sulfuric acid to enhance the growth sites for MoS2 as well as the hydrogen evolution reaction active sites for their hybrids. We demonstrate for the first time that the phase transition of VO2 at elevated temperature shows significant effect on hydrogen evolution properties of the heterostructures. Upon the phase transition of VO2, the onset potential and Tafel slope of MoS2/VO2 hybrids were dropped from 188 mV and 93 mV/dec to 99 mV and 85 mV/dec, respectively. This was attributed to the enhanced charge transport efficiency as well as interfacial strain effect on modifying the electronic structure of MoS2.

Interfacial strain effect on type-I and type-II core/shell quantum dots

A comparative experimental and theoretical study on the calculation of capped core diameter in ZnSe/ZnS, CdSe/Cd(Zn)S type-I and ZnSe/CdS type-II core/shell nanocrystals is presented. The lattice mismatch induced interface strain between core and shell was calculated from continuum elastic theory and applied in effective mass approximation method to obtain the corresponding capped core diameter. The calculated results were compared with diameter of bare cores (CdSe and ZnSe) from transmission electron microscopy images to obtain the amount of the stretched or squeezed core after deposition of tensile or compressive shells. The result of the study showed that the core is squeezed in ZnSe/ZnS and CdSe/Cd(Zn)S after compressive shell and stretched in ZnSe/CdS after tensile shell deposition. The stretched and squeezed amount of the capped core found to be in proportion with lattice mismatch amount in the core/shell structure.

Comprehensive studies of interfacial strain and oxygen vacancy on metal–insulator transition of VO2 film

As a typical strong correlation material, vanadium dioxide (VO2) has attracted wide interest due to its particular metal–insulator transition (MIT) property. However, the relatively high critical temperature (Tc) of ~68 °C seriously hinders its practical applications. Thus modulating the phase transition process and decreasing the Tc close to room temperature have been hot topics for VO2 study. In the current work, we conducted a multi-approach strategy to control the phase transition of VO2 films, including the interfacial tensile/compressive strain and oxygen vacancies. A synchrotron radiation reciprocal space mapping technique was used to directly record the interfacial strain evolution and variations of lattice parameters. The effects of interfacial strain and oxygen vacancies in the MIT process were systematically investigated based on band structure and d-orbital electron occupation. It was suggested that the MIT behavior can be modulated through the combined effects of the interfacial strain and oxygen vacancies, achieving the distinct phase transition close to room temperature. The current findings not only provide better understanding for strain engineering and oxygen vacancies controlling phase transition behavior, but also supply a combined way to control the phase transition of VO2 film, which is essential for VO2 film based device applications in the future.

The epitaxial growth and interfacial strain study of VO2/MgF2 (001) films by synchrotron based grazing incidence X-ray diffraction

High quality VO2 films with different thickness were epitaxially grown on MgF2 (001) substrates by oxide molecular beam epitaxy method. The evolution of interfacial strain was investigated by synchrotron based grazing incidence X-ray diffraction. By adjusting the incidence angles, the penetration depth of X-ray in VO2 film could be controlled and the thickness-depend lattice distortion in the epitaxial VO2 film was investigated. Due to the lattice mismatching, the pronounced tensile strain was observed in ultra-thin VO2 film. As the film thickness increasing, the interfacial strain relaxed gradually and became fully relaxed for thick VO2 films. Combined with the electric transport measurement, it was revealed that the phase transition temperature of ultra-thin VO2 film decreased greatly. The effect of interfacial strain induced phase transition modulation and the intrinsic mechanism was systematically discussed.

Electronic structure of antimonene grown on Sb2Te3 (111) and Bi2Te3 substrates

We explore the formation of single bilayer Sb(111) ultrathin film (Antimonene) on Bi2Te3 and Sb2Te3 substrates for the first time, which is theoretically predicated to be a robust trivial semiconductor but can be tuned to a 2D TI by reducing the buckling height. From angle-resolved photoemission spectroscopy measurements, the antimonene can be well grown on the two surfaces and shows clear band dispersion. The electronic structure of the antimonene shows similar character on the two surfaces, but due to the interfacial strain effect, the bands of antimonene on Bi2Te3 are flatter than on Sb2Te3, which attributes to Bi2Te3 substrate lattice constants lager than Sb2Te3. At the same time, the charge transfer effect is also observed through core level shift, which influences the band dispersion simultaneously.

Interfacial strain effect on gas transport in nanostructured electrodes of solid oxide fuel cells

Most efforts regarding strain effect at the interfaces between electrolytes and electrodes are mainly focused on enhancing the ionic conductivity in electrolytes. However, fundamental insights into the strain effect on gas transport properties in electrodes of fuel cells are still lacking. In this report, quantitative analysis is performed to evaluate the correlation between interfacial strain and the important fuel cells parameters, including limiting current density and concentration polarization. We demonstrate that the strain effect plays an important role in the performance of solid oxide fuel cells with nanostructured electrodes. Our studies provide a powerful platform for reducing concentration polarization by engineering quantitatively the interfacial strain, and facilitating the development of high-efficiency nanostructured fuel cells.

Thermal stress induced band gap variation of ZnO thin films

The growth temperature and post annealing-dependent optical and structural effect of RF magnetron sputtered ZnO thin films were examined. As the growth temperature increased, the lattice constant increased and approached the bulk value, suggesting a decrease in interfacial strain between the substrate and thin film. For the post annealed samples, the interfacial strain decreased further and was close to the bulk value regardless of the post annealing environments (in air and O2). The optical properties of all ZnO thin films examined and revealed higher transparency (>90%). Furthermore, the optical band gap varied according to the growth temperature and post annealing environments due to a decrease in the interfacial strain effect.